The present inventive subject matter relates generally to circuit breakers and methods of operating the same and, more particularly, to circuit breakers including current transformers and electronic trip units.
Circuit breakers are commonly used to protect circuitry, such as distribution wiring, from overheating due to short circuits or overloads. Circuit breakers typically include at least one set of contacts that is configured to be opened and closed by an actuator mechanism. The actuator mechanism is typically configured open and close the contacts in response to a manual or other mechanical input (e.g., by movement of a motorized actuator), and is further configured to rapidly open in response to an input from a trip unit.
Circuit breaker trip units may operate in a number of ways. For example, trip units for thermal magnetic breakers typically trip breaker contacts in response to current in and temperature of conductors in the breaker. Such trip units may use current transformers to sense currents for so-called “instantaneous” current-level tripping, and may use mechanical and/or electromechanical devices to provide thermal tripping.